1. Field of Invention
The present invention relates to an antenna apparatus. More particularly, the present invention relates to a dual purpose antenna apparatus built in a wireless communication device for supporting the purposes of the multi-band mobile phone system and the global positioning system (GPS).
2. Description of Related Art
The key development in communication technology has been the transfer from wired to wireless communication, such as by the popularization of wireless household phones and mobile phones. In the field of wireless communication, the signal is propagated in the air in the form of electromagnetic waves, where the bridge of the signals between the wireless device and the air is an antenna. That is to say, an antenna is certainly needed by a wireless communication device to transmit or receive electromagnetic waves, and is therefore an essential component of a wireless communication device.
In the conventional wireless communication device, the antenna apparatus is usually attached to the exterior of the device, such as a helix antenna attached on the exterior of a mobile phone. A variety of problems are inherent to this arrangement, however. For example, such an antenna is easily damaged by external force, the overhead of the circuit design is increased and the device is harder to carry. Furthermore, in accordance with the present design trend, many functions are integrated into a device, such as a mobile phone being able to receive and transmit signals in various frequency bands and/or having GPS functionality. Thus, the amount of components and antennas will substantially increase in the device, but the limited volume of the device must be maintained. For these reasons, the external antenna is increasingly unsuited for using in advanced wireless communication devices.
It is apparent that the compact antenna built in wireless communication devices will be a mainstream trend in the communications field. The conventional embedded compact antenna techniques comprise the flexible printed circuit (FPC), but they have some problems. Due to the FPC antenna being a kind of flat antenna, the length of the resonant path is limited within a footprint and is unable to flexibly extend, thus restricting the operating bandwidth of the FPC antenna.
This restriction becomes a great impact in a clamshell type mobile phone. In general, a clamshell type mobile phone comprises a lower cover having a keypad and an upper cover having a display. Because the antenna of the clamshell type mobile phone is often located on the top of the lower cover and near the upper cover, the center frequency of the antenna may shift due to the influence of the circuit located in the upper cover. If the center frequency of the antenna shifts out of the operating bandwidth of the system, the antenna is unable to receive and process the signals from base stations.
Moreover, the distance between the circuits located in the upper cover and the antenna is not constant, due to the folding motion of the clamshell type mobile phone. That is to say, the frequency shift value caused by the circuit located in the upper cover is also not constant. For this reason, the frequency shift is hard to be compensated for the shortness of the bandwidth in advance in an FPC antenna. The frequency shift will be more significant at low frequency than at high frequency and thus increases the degree of difficulty in designing the FPC antenna.
According to the foregoing description, an embedded compact antenna apparatus which is able to tolerate the frequency shift phenomenon is needed to ensure a good receiver sensitivity of the mobile phone apparatus, especially applying in the clamshell type mobile phone.